rFactor is a racing simulator so your bound to have many cars on the track at once, in a league i race in we use the Enduracers mod and drive for upto 12 hours per race as part of a team just like "real" endurance racing. Heres a few pics -



But.. I'm not 15 people? You download a few cars at a time, go have a drive with a friend and then you have them forever. It's what I do when me and my friends see something we want to drive, I must have 100 cars now. Sure it's not as easy as just choosing a stock car, but it's not difficult.
Oh I see what you mean. Actually you can, when you install a mod it switches to that mod as your current series, you may only use cars in that series. If you chose "all tracks and cars" when you set up the server you can jump in with every vehicle. Pretty sure that works, might be wrong.i know it isn't difficult installing them
it's just when it comes to choosing a car you cannot pick any car you have installed and race it against any other car the same way you can in forza/gt. a lot of the fun for us was racing different cars from different classes against each other.
Nice choicerFactor is a racing simulator so your bound to have many cars on the track at once, in a league i race in we use the Enduracers mod and drive for upto 12 hours per race as part of a team just like "real" endurance racing. Heres a few pics -